UV-B Induced Reprogramming of Isoflavone Biosynthesis in Soybean: From UVR8 Signaling to Functional Food Development

Isoflavones are key bioactive constituents of soybean (Glycine max L.) that contribute substantially to the nutritional and functional value of soy-based food. However, their physiological efficacy depends strongly on the chemical form, as aglycone isoflavones exhibit greater bioavailability and biological activity than glucoside, acetylglucoside and malonylglucoside conjugates. Recent advances have demonstrated that seed germination and controlled ultraviolet-B (UV-B) irradiation can synergistically enhance isoflavone biosynthesis while promoting compositional shifts from poorly absorbed conjugated forms toward highly bioavailable aglycones. Central to this response is the UV-B photoreceptor UV RESISTANCE LOCUS 8 (UVR8), which regulates phenylpropanoid and isoflavonoid metabolism through the UVR8-COP1-HY5 signaling module, together with epigenetic, hormonal, and reactive oxygen species-mediated regulatory networks. This review critically synthesizes current knowledge on the chemistry, metabolism, bioavailability and physiological significance of soybean isoflavones, with particular emphasis on germination-induced β-glucosidase activation, UV-B-mediated metabolic reprogramming and the mechanisms governing aglycone enrichment. Processing and storage strategies that affect isoflavone stability, bioaccessibility, and product quality are also evaluated, along with practical considerations for the industrial implementation of UV-B-assisted germination technologies. By integrating plant photobiology, secondary metabolism, food chemistry, processing science, and human nutrition, this review provides a comprehensive framework for developing next-generation soybean functional foods with enhanced nutritional quality, bioavailability, and commercial potential.